However, the researchers caution that indirectly comparing the two treatments may not be appropriate because “the patient cohorts were all not randomised contemporaneously and there may be confounding biases.”

In the current, prespecified analysis of STAMPEDE data, Nicholas James (University of Birmingham, UK) and team therefore analyzed outcomes for 566 patients randomly assigned to receive AAP (n=377) or DocP (n=189) during the same 17-month period to directly compare the two regimens.

During a median follow-up of 4 years, the mortality rate was 28% in the AAP arm and 23% in the DocP arm.

There was no significant difference in overall survival between the two groups, and survival was not affected by baseline metastases, which were present in 60% of patients overall.

Advertisement

There was also no significant difference between the two treatment arms in metastasis-free survival, prostate cancer-specific survival, and symptomatic skeletal events.

By contrast, there was a 49% reduced risk for treatment failure and a 35% reduced risk for disease progression among the patients receiving AAP compared with those receiving DocP.

James and team point out that the two therapies are used in different ways, with AAP given until the patient has castrate-resistant prostate cancer and DocP given as an 18-week course with the potential to use other treatment options.

They say that their data suggest that AAP improves biochemically driven outcome measures, but does not result in differences in clinical outcomes.

The fact that “the DocP cohort had more durable survival after failure, perhaps longer than before failure, may be important in counselling patients biochemically failing after DocP,” the authors write in the Annals of Oncology.

In terms of safety, the rate of grade 3 and 4 toxicity was 11% in both groups at both 1 and 2 years. However, the investigators note that the patterns of adverse events differed according to treatment. For example, febrile neutropenia was more common with DocP whereas endocrine and gastrointestinal disorders were more common with AAP.

James et al conclude: “There are now two systemic therapies, DocP and AAP, which have shown a survival benefit from randomised controlled trials when added to treatment for patients starting long-term androgen deprivation therapy for the first time.”

They add that it may now be useful to investigate “ whether a combination of AAP plus docetaxel might lead to an approximately additive benefit of using them both, further extending survival.”